A computer network is composed of a set of nodes and a set of links that connect one node to another. For instance, a computer network may be composed of a set of routers while the set of links may be cables between the routers. When a first node in the network sends a message to a second node in the network, the message may pass through many links and many nodes. The links and nodes the message passes through while traveling from the first node to the second node is referred to as a path. For example, suppose the message passes through a third node while traveling from the first node to the second node. In this case, the path leads from the first node to the third node to the second node.
Packet-based computer networks increasingly utilize label switching protocols for traffic engineering and other purposes. In a label switching network, label switching routers (LSRs) use Multi-Protocol Label Switching (MPLS) signaling protocols to establish label switched paths (LSPs). The LSRs utilize MPLS protocols to receive MPLS label mappings from downstream LSRs and to advertise MPLS label mappings to upstream LSRs. When an LSR receives an MPLS packet from an upstream router, it switches the MPLS label according to the information in its forwarding table and forwards the packet to the appropriate downstream LSR.
Links and nodes in a computer network may fail without warning. Consequently, one of the LSPs that the first node was using to communicate with the second node may stop functioning. To ensure that the first node and the second node do not send messages on a LSP that is not functioning, the nodes may periodically verify the status of the path by sending a message through the path and receiving a response through the path.
In some situations, however, verifying the connectivity along the LSPs may be difficult. For example, verifying the connectivity along the LSPs may be difficult where LSP traffic is dynamically load balanced over multiple paths using equal cost multi-path (ECMP) or other mechanisms. In this situation, verification over each of the multiple paths of an LSP may require continual use of a complex, resource intensive connectivity protocol. For example, a node may use the Label Switched Path Ping (LSP Ping) protocol to verify each of the LSPs.